In traditional supply chain inventory management, orders are the only information firms exchange, but information technology now allows firms to share demand and inventory data quickly and inexpensively. We study the value of sharing these data in a model with one supplier, N identical retailers, and stationary stochastic consumer demand. There are inventory holding costs and back-order penalty costs. We compare a traditional information policy that does not use shared information with a full information policy that does exploit shared information. In a numerical study we find that supply chain costs are 2.2% lower on averagewith the full information policy than with the traditional information policy, and themaximum difference is 12.1%. We also develop a simulation-based lower bound over all feasible policies. The cost difference between the traditional information policy and the lower bound is an upper bound on the value of information sharing: In the same study, that difference is 3.4% on average, and no more than 13.8%. We contrast the value of information sharing with two other benefits of information technology, faster and cheaper order processing, which lead to shorter lead times and smaller batch sizes, respectively. In our sample, cutting lead times nearly in half reduces costs by 21% on average, and cutting batchesin half reduces costs by 22% on average. For the settings we study, we conclude that implementing information technology to accelerate and smooth the physical flow of goods through a supply chain is significantly more valuable than using information technology to expand the flow of information.Inventory management is a commercial enterprise management of the core areas, Enterprises can also achieve an effective key, if we can achieve from the purchase of stock,Sales then the entire flow of goods and capital flow situation for the unified management and reasonable production, timely sales and inventory is the smallest. reduce the backlog of material, then the business will achieve the best results.1.sessionIn my experience, session word is probably second only to the extent of the abuse of transaction, even more interesting is the transaction and the session in the context of the meaning of some of the same.session, the Chinese often translated into the session, its original meaning refers to the beginnings and ends of a series of action / information, such as a phone call from the dial to pick up the phone to hang up the middle of the process can be described as a series of session. Sometimes we can see that the case "during the session in a browser session ,...", term used here is its original meaning, is open from a browser window to close the period of ①. The most confusing is the "user (client) during the first session," the words, it may refer to a series of user actions (generally with a specific purpose related to a series of actions, such as log on to buy goods from to sign out such an online shopping checkout process, sometimes also called a transaction), but sometimes may be just that a connection could also be that the meaning of ①, the difference can only be inferred by context ②.However, when the term session is associated with the network protocol when it often implies a "connection-oriented" and / or "on hold" so the two meanings, "connection-oriented" refers to both the communication in the communication prior to first establish a communication channel, such as phone calls, until the other party answered the phone communication can begin, and this is the opposite of writing, before you sent the letter, the time you and can not confirm the other side of the address is correct, communication channels Buyi Ding can be established,but the sender, the communication has already begun. "Keep state" means the communication party is able to associate a series of messages, making messages between each other depends, for example, a waiter can recognize old customers come back and remember the last time the customer still owes a store, dollar . Examples of this type, "a TCP session" or "a POP3 session"③.And to the web server flourishing, session in the context of semantic web development has a new expansion, its meaning is mean to the client and server to maintain state between the solution ④. Session is also sometimes used to refer to such solutions, storage structures, such "stored in the session to xxx where" ⑤. For various 用于web development languages are available to some extent on the support of such a solution, so in the context of a particular language 下, session also used to denote a solution on behalf of the language, such as regular Java in the provision of javax.servlet.http.HttpSession referred to as the session ⑥.In view of this confusion has been changed, in this article use the term session will have different meanings depending on the context, drew attention to the resolution.In this article, the use of Chinese "during the browser session," to convey the meaning of ①, use "session mechanism" to convey the meaning ④, use the "session" expression meaning ⑤, use specific "HttpSession" to convey the meaning ⑥Second, HTTP protocol and the state to maintainHTTP protocol itself is stateless, HTTP protocol which is consistent with the original purpose of the client only needs a simple request to download some file server, either the client or the server not have been necessary records of past behavior to each other, and each time between the request are independent, like a customer and a vending machine or an ordinary (non-membership) as the relationship between supermarkets.However, smart (or greedy?) People soon discovered that if they can provide on-demand generation of dynamic web information will become more useful, like a cable TV with on-demand the same function. This demand on the one hand to force gradually add HTML form, script, DOM and other client-side behavior, on the other hand there is the server-side CGI practices to respond to client-side dynamic request, the HTTP protocol as the transport carrier also added a file upload , cookie these characteristics. The role which cookie is to solve the stateless HTTP protocol efforts defects. As for the subsequent emergence of the session mechanism is yet another in between the client and the server state solution.Let us use some examples to describe the session cookie and the differences and similarities between the mechanisms. I once frequented a coffee shop with free gifts to drink five cups of coffee offers a cup of coffee, but a one-time consumption of five cups of coffee is remote, then need a way to record a customer's consumption. Imagine that in fact nothing less than the following several options:1, the store's staff is very powerful, able to remember each customer's consumption, as long as customers entered the cafe, shop assistants know how to deal with the. This approach is the agreement itself to support the state.2, issue customers a card recording the number of consumers in general have a validity period. Each consumer, if this card is produced, then the consumer will be with the consumer before or after linking up. This approach is maintained in the client state.3, a membership card issued to customers, in addition to any information outside the card number is not recorded, each consumer, if the card is produced, then the records clerk in the store to find the card number corresponds to the record to add some consumer information. Thisapproach is maintained in the server-side state.As the HTTP protocol is stateless, but due to various considerations do not want to become a state, therefore, the last two programs has become a realistic option. Specifically cookie mechanism is used to maintain state of the client program, which uses a session mechanism to maintain state in the server-side program. We also see that, thanks to server-side maintain state of the program in customer client but also Xuyaobaocun a logo, so mechanisms may need the help of session cookie mechanism to identify the purpose of Da Dao saved, it actually alternatives are available.Third, the cookie mechanismThe basic principle cookie mechanism as simple as the above example, but there are several issues to resolve: "membership card" how to distribute; "membership card" of the content; and customers how to use the "Member Card."Orthodox cookie distribution is by extending the HTTP protocol to achieve, and the server through the HTTP response header with a line of special instructions to prompt the browser in accordance with the instructions generates the corresponding cookie. But pure client-side scripting such as JavaScript or VBScript can also generate the cookie.The cookie used by the browser in the background according to certain principles automatically sent to the server. Check all stored browser cookie, if a cookie is greater than or equal scope statement will be the location of the requested resources, put the resources of the HTTP request cookie attached to the head sent the request to the server. Means that McDonald's membership card can only be produced in the McDonald's store, if a store has also issued its own membership card, then enter the store when the addition to produce McDonald's membership card, but also to produce a member of the store card.cookie's contents include: name, values, expiration time, path and domain.You can specify a domain in which a domain such as. , the equivalent of main store signs, such as Procter & Gamble, you can also specify a specific domain of a machine under such or , can float Flexibility to do than.Path is the name behind the URL with the path, such as / or / foo, etc., can do more than a counter Rejoice.Path together with the domain constitutes a cookie's scope. If you do not set the expiration time, then the lifetime of this cookie to the browser during the session, simply close the browser window, cookie disappears. This period of life of the cookie browser session is called session cookie. Session cookie is generally not stored on the hard disk but kept in memory, of course, provided that it is not standardized. If you set the expiration time, the browser the cookie will be saved to the hard disk, open again after closing the browser, the cookie is still valid until the expiration time exceeds a set.Stored in a cookie on your hard disk in a different browser, shared between processes, such as the two IE windows. And stored in memory for the cookie, different browsers have different approaches. For IE, open windows in a press Ctrl-N (or from the File menu) to open the window can be shared with the original window while using other means to open the IE process will not have to open the windows shared memory cookie; for Mozilla Firefox0.8, all of the process and can share the same tab the cookie. In general is the window.open javascript window will open with the original windows shared memory cookie. Browser, this cookie for the session cookiedoes not believe that people only recognize the approach to the use of the regular session of web application development mechanism causing great distress.Here is a goolge set cookie response header exampleHTTP/1.1 302 FoundLocation: /intl/zh-CN/Set-Cookie: PREF = ID = 0565f77e132de138: NW = 1: TM = 1098082649: LM = 1098082649: S = KaeaCFPo49RiA_d8; expires = Sun, 17-Jan-2038 19:14:07 GMT; path = /; domain =. google . comContent-Type: text / htmlThis is the use of HTTPLook the HTTP Sniffer HTTP communications software to capture the part of the recordGoolge browser to access the resources again, automatically send out cookieUse Firefox can easily observe the current value of cookieUse HTTPLook with Firefox cookie can easily understand the working principle.IE can be set to ask before accepting cookieThis is a dialog box asking to accept cookie.Fourth, understand the session mechanismmechanism is a server-side session mechanism, the server uses a hash table is similar to the structure (and probably is to use a hash table) to save the information.When the program needs for a client's request to create a session when the server first checks the client's request is included in a session ID - known as the session id, if the description contains a session id for this client previously Create over session, the server in accordance with the session id to retrieve the session out of the use (if not retrieved, may be the new one), if the client request does not include session id, then create a session for this client and generate a session with this associated with the session id, session id value should be a not only will not repeat, not easy to find the law to copy the string, the session id to be returned in this response to the client saved.Save the session id of the ways to use cookie, so the interaction of the browser can automatically identify this play by the rules to the server. The name of this cookie are generally similar to SEEESIONID, and. For example, web applications weblogic generated cookie, JSESSIONID = ByOK3vjFD75aPnrF7C2HmdnV6QZcEbzWoWiBYEnLerjQ99zWpBng! -145788764, Its name is JSESSIONID.As the cookie can be artificially prohibited, there must be other mechanisms to be banned in the cookie when the session id still be able to pass back to the server. Often use a technique called URL rewriting, the session id is attached to the URL path directly behind, there are two additional ways, one is the URL path as additional information, showing the form of http:// ... .. / xxx; jsessionid = ByOK3vjFD75aPnrF7C2HmdnV6QZcEbzWoWiBYEnLerjQ99zWpBng! -145788764 The other is as a URL query string appended to the back, showing the form of http://.. (xxx)jsessionid=ByOK3vjFD75aPnrF7C2HmdnV6QZcEbzWoWiBYEnLerjQ99zWpBng!-145788764Both ways is no different for users, and only a server parsing the time to deal with the different ways, using the first ways are conducive to turning one kind of session id's information and to distinguish normal program parameters.Wei Liao Zai the interaction always maintain state, we must each client may request a path to the rear of containing this session id.Another technique known as hidden form fields. Is that the server will automatically modify the form, add a hidden field, so when the form is submitted to the session id passed back to the server. Example, the following form<form name="testform" action="/xxx"><input type="text"></ Form>Being passed to client will be rewritten before<form name="testform" action="/xxx"><input type="hidden" name="jsessionid"value="ByOK3vjFD75aPnrF7C2HmdnV6QZcEbzWoWiBYEnLerjQ99zWpBng!-145788764"><input type="text"></ Form>Application of this technology is now less, I contacted the very old iPlanet6 (SunONE Application Server's predecessor) on the use of this technology.In fact this technology can simply apply to the action URL rewriting instead.When talking about the session mechanism, often heard of such a misunderstanding, "as long as the browser is closed, session disappears." In fact, imagine the example card, unless the customer to make sales on the store card, otherwise the store would not easily remove the customer information. This is also true of the session, unless the procedure to inform the server to delete a session, otherwise the server will remain on the program are generally done in the user log off when the send a command to delete the session. However, the browser will never take the initiative to notify the server will be shut off, so the server will not have the opportunity to know the browser has been the reason why there is such a misconception, the majority of session mechanism to use a session cookie to store the session id and close your browser the session id is gone, once again connect to the server will not be able to find when the original session. If the server cookie settings are saved to the hard disk, or use some means to rewrite the browser's HTTP request header sent to the original session id sent to the server, then re-open the browser can still find the original session.It is precisely because of the closure does not cause the browser session is deleted, forcing server seesion set up a failure time, as the distance between the first use of the client session for more than the failure time, the server that the client has ceased its activities, the session will be deleted to save storage space.5, javax.servlet.http.HttpSessionHttpSession session mechanism is the Java platform implementation of norms, because it isonly the interface, specific to each web application server providers, in addition to standard support, there will still be no requirement of some norms in the nuances. Here we are with BEA's Weblogic Server8.1 as an example to demonstrate.First of all, Weblogic Server provides a set of parameters to control its HttpSession implementation, including the use of cookie switch option to use URL rewriting switches, session persistence settings, session failure time setting, as well as for the cookie a variety of settings, such as set cookie name, path, domain, cookie survival time.In general, session are stored in memory, when the process is stopped, or restart the server when the memory of the session will also be empty, if you set the session persistence feature, the server will save the session to your hard drive When the server process restart or the information can be used again, Weblogic Server supports sustainable manner including documents, databases, client-side cookie preservation and reproduction.Strictly speaking not a persistent copy saved, because the session is actually stored in memory, but the same information is replicated to each server process within the cluster, so even if a server process to stop working and still available from other processes obtain session.cookie settings will affect the survival time of the browser generates a session cookie is a cookie. The default is to use a session cookie. Interested can use it to test us in the fourth quarter, as mentioned in the misunderstanding.cookie path for the web application is a very important option, Weblogic Server on the default handling of this option makes it significantly different from other servers. We will discuss the topic later.Settings on the session reference [5] /wls/docs70/webapp/weblogic_xml.html # 10368696, HttpSession Frequently Asked Questions (In this section the implications for the session mixed ⑤and ⑥)1, session is created whenA common misconception is that the session in a client visit, was created, but the fact is that until a server-side program called HttpServletRequest.getSession (true) when such a statement is created, note that if the JSP does not appear to use <% @ page session = "false"%> closed session, the JSP file will be automatically compiled into a Servlet when the inclusion of such a statement HttpSession session = HttpServletRequest.getSession (true); This is also implied in JSP session object origin.As the session will consume memory resources, so if you do not intend to use the session, all the JSP should be turned off it.2, session is deleted whenComprehensive discussions earlier, session is deleted in the following cases a. program calls HttpSession.invalidate (); or b. from the last time before the client sends the session id than the interval session timeout settings; or c. server process is stopped (non-persistent session)3, how to do delete the browser closed session。
